Free energy cavity formation

To quantify the difference in the free energies of formation of a cavity and in capabilities of water to participate in van der Waals interactions with a solute it has been suggested 104,105) to use the free energy of interphase transfer of a CH2 group. To quantify the difference in the capability of water in the phases to participate in electrostatic interactions with a solute, it has been proposed 11,106> to use the logarithm of the partition coefficient of Na-salt of DNP-glycine. 

The free energy of the cavity formation, AG v, was calculated proceeding from the scaled particle theory (SPT) [52,53]. According to this theory, the free energy of formation of a spherical cavity is given by the following formula... 

The comparison between the two processes (Eqns. 74 and 75) involves several changes in interaction energies. As the initial state is the same in the two systems, changes in energy when the solute is removed from water will be the same in each case. When a solute is transferred to a non-polar liquid (Eqn. 75) there is a gain of solute-solvent interactions and a loss of solvent-solvent interactions, which is equivalent to the free energy of formation of a cavity in the solvent of a suitable size to accommodate the solute molecule. 

Where AG is the free energy term associated with cavity formation, N is Avogadro s number, AA is the change in surface area due to... 

The nonelectrostatic components of the free energy such as the energy of cavity formation AGcav or components that take into account atomistic details of the medium (interactions between atoms inside the cavity and those in the medium) are calculated using empirical approximations (see Reference 164 for review or 165 for recent developments). These terms are do not affect the SCF procedure since their dependence on electron density p is usually neglected. 

The first step corresponds to the formation of a Lennard-Jones cavity with the shape of the solute the charges are included in the second step. This free energy decomposition is, of course, path dependent different (divergent) results would be obtained if the electrostatic coupling were included first. 

Our extension of the LIE approach to calculate free energies of hydration (AGhyd) incorporated a third term proportional to the solute s solvent-accessible surface area (SASA), as an index for cavity formation within the solvent.19,27 The latter term is needed for cases with positive AGhyd such as alkanes and additional improvement occurred when both a and P were allowed to vary. Equation 8 gives the corresponding LIE/SA equation for... 

The dynamic NMR technique allows investigations on the rate of exchange between 3-substituted quinuclidinium ions and water. The rate of dissociation of amine/water (or amine/alcohol) complexes is determined71 by the free energy contribution from the pKa-dependent hydrogen bond breaking, and from dispersion forces between acceptor and donor which may be at the most 40% of the activation energy of the dissociation of the complex. Similar importance may be attributed to a term for the formation of a cavity prior to the dissociation of the complexes. 

Qausius-Mosotti ftmction for species i, Eq. (42) free energy of cavity formation, Eqs. (20). (22)... 

Formation constant, apparent, 234 of complexes in the mobile phase, 232 Free energy change, 204 for cavity formation in liquid, 204-203 for electrostatic interactions, 208-211 entropic contributions. 212 for retention, 211... 

Equation (22) has been found to be somewhat more useful than Eq. (20) for evaluation of the free energy change related to caSdty formation when more than one solute species is present. In the form given by Eq. (22) the cavity term can be c culated if macroscopic sur K e tension, y, K, and molecular surface area of both the solute and solvent are known. The latter values may be calculated for spherical or quasi-spherical mole- cules as... 

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